Electric shock drowning causes multiple fatalities every year, most commonly in bodies of fresh water. It is caused by the presence of dangerous electric currents in the water. Most often, the dangerous currents are alternating current, but direct currents can be dangerous too. These currents may be discharged into the water from numerous sources, such as from an extension cord dropped into the water, faulty wiring on a residential or commercial dock, or shorts in the wiring of a vessel or a fixture (e.g. an underwater light). When a person in freshwater is exposed to an electrical current, the current tends to flow through the human body because the body has less resistance than the surrounding water. An alternating current that passes through the body paralyzes the muscles, causing the person to sink and drown. In some instances, the voltage in the water (whether from direct or alternating current) may also be great enough that the shock causes death.
To address this danger, various devices or systems have been developed to detect the presence of conditions that may cause electrical shock drowning. These systems most often work by detecting a voltage, voltage gradient, or current in the water. If the voltage or gradient exceeds a preset threshold, the system triggers an alarm or another indicator to alert of the dangerous condition.
Although these systems are able to detect stray currents in some environments, their effectiveness is limited by various factors. One limitation arises due to the difficulty in controlling for false alarms. Environments typically include a certain amount of background noise with respect to the voltage or current detected in the water, but the exact amount of noise varies between environments and even locations in a particular environment. Systems attempt to account for this noise by having a static trigger threshold, which is preselected to balance the risk of false alarms with the risk of failing to detect a dangerous condition. This static, one-size-fits-all approach, however, fails to account for a system's specific operating environment. In high noise environments, the system may be more likely to trigger false alarms. In low noise environments, the system may fail to trigger an alarm even though a detected voltage or current clearly exceeds the background noise.
A second, related limitation is the relatively small, and usually unknown, detection range of the systems. Depending on the mineral content and other factors that affect the conductivity of water, voltage and current dissipate quickly. So the further an electrical source is from the system, the less voltage or current that will be detected by the system. As a result, at a certain distance, the magnitude of the voltage or current from an electrical source becomes difficult to distinguish from noise and will not exceed the preset threshold. Often, the effective range of these systems is approximately 20 feet or less. But as with noise, the effective range can vary significantly depending on the environment. In some environments, the effective range may be significantly greater, but in many others, it will be significantly less. Unfortunately, users usually have no way of knowing the effective range in a specific environment.
The limitations associated with false alarms and detection ranges are further exacerbated by the limitations associated with commercially affordable equipment. In order to keep the price of systems within commercially viable price points, components must be selected with price in mind. These commercially viable systems ordinarily have a sensitivity of approximately 2 millivolts. To achieve greater sensitivity, more precise components would be required and are typically much more costly. So even where it may be theoretically possible to improve the sensitivity of the system, there is a practical limitation on sensitivity that cannot be avoided without significantly increasing costs.
Further, many systems may be impacted by their connection to a main power source, such as the electrical circuit on a dock (rather than a battery). Although such an installation can be advantageous because it provides continuous power to the system, it may affect the performance of the system. In many cases, these systems use the ground of the main power as a reference for zero. But in the event of any faults associated with the main power source, such as the presence of a charge on the ground, the system may fail to detect dangerous currents or trigger false alarms.
Even where a system does detect a dangerous condition, it may take insufficient action. In most systems, the system provides only a visual alarm, an audible alarm, or perhaps both. Such an alarm may be sufficient if a user is in the immediate vicinity and not already in the water. But if the user is not around, he may never know that a dangerous condition existed. Particularly if the dangerous condition is intermittent, the user may be unsuspecting the next time he enters the water. Likewise, if a user is already in the water when the system alarms, the visual or audible alarm does little to protect the user from the dangerous condition.
Consequently, there is a need in the art for a shock detection device and methods that do not suffer the limitations that are inherent in detecting electrical sources based on voltage or current. Preferably, the device and methods would allow for more reliable detection of dangerous alternating currents, while also providing detection at greater ranges. Even more preferably, the device and methods may include dynamic self-configuration based on specific operating environments, and in some cases, users may even be alerted about the detection range of the device. The device may also be capable of being connected to a main power supply without impairing its detection circuit, may provide more remote notifications to users, and may disable known power sources.